Hexasubstituted Benzenes with Ultrastrong Dipole Moments

Functionalized Phenanthrene Imide-Based Polymers for n-Type Organic Thin-Film Transistors

High-performing n-type polymers are crucial for the advance of organic electronics field, however strong electron-deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide-functionalized polycyclic aromatic hydrocarbons (PAHs) with extended π-conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high-performance n-type polymers. Among the PAHs, phenanthrene (PhA) features a well-delocalized aromatic π-system with multiple modifiable active sites . However, the PhA-based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we report two functionalized PhAs, CPOI and CPCNI, by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA. Notably, the dicyanomethylene-modified CPCNI exhibits a well stabilized LUMO energy level (-3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI, two polymers PCPOI-Tz and PCPCNI-Tz were developed. Applied to organic thin-film transistors, owing to the strong electron-deficiency of CPCNI, polymer PCPCNI-Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI-Tz. This work affords two structurally novel electron-deficient building blocks and highlights the effectiveness of dual functionalization of PhAs with strong electron-withdrawing groups for devising n-type polymers.

Computational Study of Ground-State Destabilization Effects and Dipole-Dipole Interaction Energies in Amphidynamic Crystals

Ground-state destabilization is a promising strategy to modulate rotational barriers in amphidynamic crystals. Density functional theory studies of polar phenylenes installed as rotators in pillared paddle-wheel metal organic frameworks were performed to investigate the effects of ground-state destabilization on their rotational dynamics. We found that as the steric size of phenylene substituents increases, the ground-state destabilization effect is also increased. Specifically, a significant destabilization of the ground-state energy occurred as the size of the substituents increased, with values ranging from 2 to 11.7 kcal/mol. An evaluation of the effects of substituents on dipole-dipole interaction energies and rotational barriers suggests that it should be possible to engineer amphidynamic crystals where the dipole-dipole interaction energy becomes comparable to the rotational barriers. Notably, while pure dipole-dipole interaction energies reached values ranging from 0.6 to 2.4 kcal/mol, the inclusion of electronic and steric effects can alter dipolar orientations to significantly greater values. We propose that careful selection of polar substituents with different sizes may help create temperature-responsive materials with switchable collective polarization.

A Terrylene-Anthraquinone Dyad as a Chromophore for Photothermal Therapy in the NIR-II Window

A terrylenedicarboximide-anthraquinone dyad, FTQ, with absorption in the second near-infrared region (NIR-II) is obtained as a high-performance chromophore for photothermal therapy (PTT). The synthetic route proceeds by C-N coupling of amino-substituted terrylenedicarboximide (TMI) and 1,4-dichloroanthraquinone followed by alkaline-promoted dehydrocyclization. FTQ with extended π-conjugation exhibits an optical absorption band peaking at 1140 nm and extending into the 1500 nm range. Moreover, as determined by dielectric spectroscopy in dilute solutions, FTQ achieves an ultrastrong dipole moment of 14.4 ± 0.4 Debye due to intense intramolecular charge transfer. After encapsulation in a biodegradable polyethylene glycol (DSPE-mPEG2000), FTQ nanoparticles (NPs) deliver a high photothermal conversion efficiency of 49% under 1064 nm laser irradiation combined with excellent biocompatibility, photostability, and photoacoustic imaging capability. In vitro and in vivo studies reveal the great potential of FTQ NPs in photoacoustic-imaging-guided photothermal therapy for orthotopic liver cancer treatment in the NIR-II window.

Effect of Fluoride Atoms on the Electrochemical Performance of Tetracyanoquinodimethane(TCNQ) Electrodes in Zinc-ion Batteries

Tetracyanoquinodimethane (TCNQ) electrode material has achieved excellent performance in aqueous zinc-ion batteries (AZIBs). However, fundamental understanding about effect of substitutes on electrochemical performance of TCNQ remain unknown. In this work, the effects of fluorine (F) as an electron-absorbing group on the structure, morphology and electrochemical performance of TCNQ and storage mechanism of TCNQ in AZIBs are discussed. Theoretical calculation proves that the introduction of fluorine atoms decreases lowest unoccupied molecular orbital (LUMO) energy of TCNQ thus affect the redox potential. Electrochemical performance of TCNQ/Fluoro-7,7,8,8-tetracyanoquinodimethane (FTCNQ)/2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4 TCNQ) is evaluated from 25 °C to -20 °C in AZIBs. Results tend out that with the increasing substituents of F on TCNQ molecular, their stability in AZIBs decrease. Dipole moment calculation further shows that the introduction of fluorine atoms is inconducive to the stability of the electrode material in aqueous solution. Ex-situ characterization demonstrate that electron withdrawing groups do not change the REDOX center of TCNQ electrode materials. Our work provides a new thought for the selection of the electrode material in AZIBs.

Electric Field-Induced Nano-Assembly Formation: First Evidence of Silicon Superclusters with a Giant Permanent Dipole Moment

The outstanding properties of silicon nanoparticles have been extensively investigated during the last few decades. Experimental evidence and applications of their theoretically predicted permanent electric dipole moment, however, have only been reported for silicon nanoclusters (SiNCs) for a size of about one to two nanometers. Here, we have explored the question of whether suitable plasma conditions could lead to much larger silicon clusters with significantly stronger permanent electric dipole moments. A pulsed plasma approach was used for SiNC production and surface deposition. The absorption spectra of the deposited SiNCs were recorded using enhanced darkfield hyperspectral microscopy and compared to time-dependent DFT calculations. Atomic force microscopy and transmission electron microscopy observations completed our study, showing that one-to-two-nanometer SiNCs can, indeed, be used to assemble much larger "superclusters" with a size of tens of nanometers. These superclusters possess extremely high permanent electric dipole moments that can be exploited to orient and guide these clusters with external electric fields, opening the path to the controlled architecture of silicon nanostructures.

Unraveling the Role of Non-Fullerene Acceptor with High Dielectric Constant in Organic Solar Cells

Increasing the relative dielectric constant is a constant pursuit of organic semiconductors, but it often leads to multiple changes in device characteristics, hindering the establishment of a reliable relationship between dielectric constant and photovoltaic performance. Herein, a new non-fullerene acceptor named BTP-OE is reported by replacing the branched alkyl chains on Y6-BO with branched oligoethylene oxide chains. This replacement successfully increases the relative dielectric constant from 3.28 to 4.62. To surprise, BTP-OE offers consistently lower device performance relative to Y6-BO in organic solar cells (16.27% vs 17.44%) due to the losses in open-circuit voltage and fill factor. Further investigations unravel that BTP-OE has resulted in reduced electron mobility, increased trap density, enhanced first order recombination, and enlarged energetic disorder. These results demonstrate the complex relationship between dielectric constant and device performance, which provide valuable implications for the development of organic semiconductors with high dielectric constant for photovoltaic application.

Supramolecular Weaving by Halogen-Bonding in Functionality-Rich Hexasubstituted Aromatic Synthons

Hexasubstituted benzenes are interesting platforms for the generation of functional materials, whose applications span from supramolecular recognition to organic electronics. Their synthesis is difficult to achieve by controlling multiple substitution steps of all hydrogen atoms on the aromatic benzene skeleton, so, often, cycloaddition reactions from disubsituted alkynes are used. In this work, we report a novel, straightforward route to C₃-symmetrical hexasubstituted aromatic synthons with a diverse and rich pattern of functionalities, and we report about their packing mode in the crystals, in which, unprecedentedly, directional, strong halogen bonding interactions are capable of forming bidimensional supramolecular weaving.

Polyhalogenated aminobenzonitriles vs. their co-crystals with 18-crown-6: amino group position as a tool to control crystal packing and solid-state fluorescence

Strengthening (para-isomers) or weakening (ortho-isomers) of π-electron aggregation due to the crystal structure rearrangement results in the bathochromic or hypsochromic shift of the fluorescence maximum.

Effect of electron-withdrawing fluorine and cyano substituents on photovoltaic properties of two-dimensional quinoxaline-based polymers

In this study, strong electron-withdrawing fluorine (F) and cyano (CN) substituents are selectively incorporated into the quinoxaline unit of two-dimensional (2D) D-A-type polymers to investigate their effects on the photovoltaic properties of the polymers. To construct the 2D polymeric structure, electron-donating benzodithiophene and methoxy-substituted triphenylamine are directly linked to the horizontal and vertical directions of the quinoxaline acceptor, respectively. After analyzing the structural, optical, and electrochemical properties of the resultant F- and CN-substituted polymers, labeled as PBCl-MTQF and PBCl-MTQCN, respectively, inverted-type polymer solar cells with a non-fullerene Y6 acceptor are fabricated to investigate the photovoltaic performances of the polymers. It is discovered that the maximum power conversion efficiency of PBCl-MTQF is 7.48%, whereas that of PBCl-MTQCN is limited to 3.52%. This significantly reduced PCE of the device based on PBCl-MTQCN is ascribed to the formation of irregular, large aggregates in the active layer, which can readily aggravate the charge recombination and charge transport kinetics of the device. Therefore, the photovoltaic performance of 2D quinoxaline-based D-A-type polymers is significantly affected by the type of electron-withdrawing substituent.

Asymmetric Glycolated Substitution for Enhanced Permittivity and Ecocompatibility of High-Performance Photovoltaic Electron Acceptor

Traditional organic photovoltaic materials exhibit low dielectric constants (εr) of 3 to 4, restricting the further enhancement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). Herein we design and synthesize a fused-ring electron acceptor named Y6-4O through introducing an asymmetric highly polarizable oligo(ethylene glycol) side chain onto the pyrrole unit of Y6. Compared with alkylated Y6 (εr = 3.36), asymmetric glycolated Y6-4O shows a notably higher εr value of 5.13 and better solubility in nonhalogen solvents. Because of the higher εr value, the devices based on as-cast PM6:Y6-4O processed using toluene exhibit a higher charge separation yield, slower bimolecular recombination kinetics, and less voltage loss relative to the control devices based on PM6:Y6. Consequently, a high PCE of 15.2% is achieved for PM6:Y6-4O-based devices, whereas the PM6:Y6-based devices show PCEs of only 7.38%. 15.2% is the highest PCE for the as-cast nonhalogenated processed OSC devices, and it is also much higher than the values (<8.5%) reported for OSCs based on high-permittivity (εr > 5) organic photovoltaic semiconductors.

GaSeCl5O: A Molecular Compound with Very Strong SHG Effect

GaSeCl₅O is a new inorganic molecular compound prepared from SeO₂, SeCl₄, and GaCl₃ at 50 °C in quantitative yield. The structure of the title compound is described by GaCl₃(OSeCl₂) molecules with a tetrahedrally coordinated Ga atom and a pseudo-tetrahedrally coordinated Se atom (including lone pair of Se(IV)) that are bridged by oxygen. GaSeCl₅O crystallizes in the polar chiral space group P6₁, which is rarely observed for molecular structures. The compound is characterized by X-ray structure analysis based on single crystals and powder samples, thermogravimetry, infrared and Raman spectroscopy as well as by second harmonic generation (SHG) measurements. The experimental data are complemented by density functional theory calculations. GaSeCl₅O shows one of the strongest SHG signals known in the visible part of the electromagnetic spectrum (480-700 nm) with an SHG intensity 10 times higher than potassium dihydrogen phosphate (KDP). This is in accordance with the phase matchability and a strong dipole moment (|μ| = 8.3 D for a molecule in the crystal lattice). Such a strong SHG effect is also remarkable since GaSeCl₅O-unlike most of the materials with strong SHG intensity-is an inorganic molecular compound.

Cyano-Functionalized Quinoxaline-Based Polymer Acceptors for All-Polymer Solar Cells and Organic Transistors

Quinoxaline (Qx) derivatives are promising building units for efficient photovoltaic polymers owing to their strong light absorption and high charge-transport abilities, but they have been used exclusively in the construction of polymer donors. Herein, for the first time, Qx-based polymer acceptors (P_A s) were developed by introducing electron-withdrawing cyano (CN) groups into the Qx moiety (QxCN). A series of QxCN-based P_A s, P(QxCN-T2), P(QxCN-TVT), and P(QxCN-T3), were synthesized by copolymerizing the QxCN unit with bithiophene, (E)-1,2-di(thiophene-2-yl)ethene, and terthiophene, respectively. All of the P_A s exhibited unipolar n-type characteristics with organic field-effect transistor (OFET) mobilities of around 10^-2  cm²  V^-1  s^-1 . In space-charge-limited current devices, P(QxCN-T2) and P(QxCN-TVT) exhibited electron mobilities greater than 1.0×10^-4  cm²  V^-1  s^-1 , due to the well-ordered structure with tight π-π stacking. When the P_A s were applied in all-polymer solar cells (all-PSCs), the highest performance of 5.32 % was achieved in the P(QxCN-T2)-based device. These results demonstrate the significant potential of Qx-based P_A s for high-performance all-PSCs and OFETs.

Black HPHAC: Synthesis and properties of dinitroHPHAC and its reduced global aromaticity in the dication state

Introduction of functional groups on a [Formula: see text]-conjugated system is one of the most promissing methods to modulate their chemical and physical properties. Here, dinitrohexapyrrolohexaazacoronene (dinitroHPHAC) was synthesized, in which two nitro groups are introduced at the same pyrrole ring. The dinitroHPHAC possesses a large dipole moment ([Formula: see text] = 11.7 D at B3LYP/6-31G(d,p)) and showed solvatochromism with decreased HOMO-LUMO energy gap. Interestingly, the colour of the solid is black to the naked eye. The global aromaticity of the dication state is decreased compared with those of pristine HPHAC and mononitroHPHAC.

Polarity Matters: Dielectric Relaxation in All-cis-Multifluorinated Cycloalkanes

The polarity of all-cis-multifluorinated cyclohexanes can be fine-tuned by the number and relative orientation of fluoro substituents, giving rise to a series of compounds with strong dipole moments. Simulations provided the energetics, the dipole moments, and the respective molecular polarizabilities, while dielectric spectroscopy gave information on the dielectric permittivities and the molecular dynamics. In special cases, dipole moments in excess of 6 D and dielectric permittivities of over 300 were obtained by simulation and experiment. Melting temperatures within a given family of multifluorinated cyclohexanes were found to scale with the molecular volume. The less-symmetric all-cis-octafluorotetrahydronaphthalene did not readily crystallize, permitting an investigation of the molecular dynamics in an energetically unfavorable yet rigid and facially polarized isomer. The resulting dynamics above the glass temperature conform to the structural α-relaxation and to the celebrated Johari-Goldstein β-relaxation.

Electronic, molecular, and solid-state structural effects of strong electron withdrawing and donating groups in functionalized fluorophthalonitriles

Perfluoro phthalonitrile substituted separately with perfluoroalkyl (EWG) and NH2, NHMe, and NMe2 (EDG) groups generate a series of aromatic C-H bonds-free nitriles that can now lose electrons, whose HOMO–LUMO gap is narrowed by EDG beyond the level induced by EWG, and whose dipole moments double. Molecular parameters vary linearly with Hammett’s free-energy constants, their electronic underpinning being uncovered by DFT calculations. The phthalonitriles’ assembling in solid-state structures is determined by forces that transition from van der Waals, in the case of EWG, to H-bonding and/or [Formula: see text]-stacking interactions in the case of EDG, as revealed by their single-crystal X-ray structures.

Cyano-Functionalized Bithiophene Imide-Based n-Type Polymer Semiconductors: Synthesis, Structure-Property Correlations, and Thermoelectric Performance

n-Type polymers with deep-positioned lowest unoccupied molecular orbital (LUMO) energy levels are essential for enabling n-type organic thin-film transistors (OTFTs) with high stability and n-type organic thermoelectrics (OTEs) with high doping efficiency and promising thermoelectric performance. Bithiophene imide (BTI) and its derivatives have been demonstrated as promising acceptor units for constructing high-performance n-type polymers. However, the electron-rich thiophene moiety in BTI leads to elevated LUMOs for the resultant polymers and hence limits their n-type performance and intrinsic stability. Herein, we addressed this issue by introducing strong electron-withdrawing cyano functionality on BTI and its derivatives. We have successfully overcome the synthetic challenges and developed a series of novel acceptor building blocks, CNI, CNTI, and CNDTI, which show substantially higher electron deficiencies than does BTI. On the basis of these novel building blocks, acceptor-acceptor type homopolymers and copolymers were successfully synthesized and featured greatly suppressed LUMOs (-3.64 to -4.11 eV) versus that (-3.48 eV) of the control polymer PBTI. Their deep-positioned LUMOs resulted in improved stability in OTFTs and more efficient n-doping in OTEs for the corresponding polymers with a highest electrical conductivity of 23.3 S cm^-1 and a power factor of ∼10 μW m^-1 K^-2. The conductivity and power factor are among the highest values reported for solution-processed molecularly n-doped polymers. The new CNI, CNTI, and CNDTI offer a remarkable platform for constructing n-type polymers, and this study demonstrates that cyano-functionalization of BTI is a very effective strategy for developing polymers with deep-lying LUMOs for high-performance n-type organic electronic devices.

Promoting charge separation in donor–acceptor conjugated microporous polymers via cyanation for the photocatalytic reductive dehalogenation of chlorides

Conjugated microporous polymers (CMPs) have emerged as promising heterogeneous photocatalysts for organic transformations owing to their structural designability and functional versatility.

Co-crystals of polyhalogenated diaminobenzonitriles with 18-crown-6: effect of fluorine on the stoichiometry and supramolecular structure

Fluorine in the ortho-position of diaminobenzonitrile promotes the formation of the N–H⋯NC bond which results in a 3D supramolecular structure of the co-crystal.

2D Inorganic Bimolecular Crystals with Strong In-Plane Anisotropy for Second-Order Nonlinear Optics

2D inorganic bimolecular crystals, consisting of two different inorganic molecules, are expected to possess novel physical and chemical properties due to the synergistic effect of the individual components. However, 2D inorganic bimolecular crystals remain unexploited because of the difficulties in preparation arising from non-typical layered structures and intricate intermolecular interactions. Here, the synthesis of 2D inorganic bimolecular crystal SbI₃ ·3S₈ nanobelts via a facile vertical microspacing sublimation strategy is reported. The as-synthesized SbI₃ ·3S₈ nanobelts exhibit strong in-plane anisotropy of phonon vibrations and intramolecular vibrations as well as show anisotropic light absorption with a high dichroism ratio of 3.9. Furthermore, it is revealed that the second harmonic generation intensity of SbI₃ ·3S₈ nanobelts is highly dependent on the excitation wavelength and crystallographic orientation. This work can inspire the growth of more 2D inorganic bimolecular crystals and excite potential applications for bimolecular optoelectronic devices.

Enhancing the Open-Circuit Voltage of Perovskite Solar Cells by Embedding Molecular Dipoles within Their Hole-Blocking Layer

Engineering the energetics of perovskite photovoltaic devices through deliberate introduction of dipoles to control the built-in potential of the devices offers an opportunity to enhance their performance without the need to modify the active layer itself. In this work, we demonstrate how the incorporation of molecular dipoles into the bathocuproine (BCP) hole-blocking layer of inverted perovskite solar cells improves the device open-circuit voltage (V_OC) and, consequently, their performance. We explore a series of four thiaazulenic derivatives that exhibit increasing dipole moments and demonstrate that these molecules can be introduced into the solution-processed BCP layer to effectively increase the built-in potential within the device without altering any of the other device layers. As a result, the V_OC of the devices is enhanced by up to 130 mV, with larger dipoles resulting in higher V_OC. To investigate the limitations of this approach, we employ numerical device simulations that demonstrate that the highest dipole derivatives used in this work eliminate all limitations on the V_OC stemming from the built-in potential of the device.

A Narrow-Bandgap n-Type Polymer Semiconductor Enabling Efficient All-Polymer Solar Cells

Currently, n-type acceptors in high-performance all-polymer solar cells (all-PSCs) are dominated by imide-functionalized polymers, which typically show medium bandgap. Herein, a novel narrow-bandgap polymer, poly(5,6-dicyano-2,1,3-benzothiadiazole-alt-indacenodithiophene) (DCNBT-IDT), based on dicyanobenzothiadiazole without an imide group is reported. The strong electron-withdrawing cyano functionality enables DCNBT-IDT with n-type character and, more importantly, alleviates the steric hindrance associated with typical imide groups. Compared to the benchmark poly(naphthalene diimide-alt-bithiophene) (N2200), DCNBT-IDT shows a narrower bandgap (1.43 eV) with a much higher absorption coefficient (6.15 × 10⁴ cm^-1 ). Such properties are elusive for polymer acceptors to date, eradicating the drawbacks inherited in N2200 and other high-performance polymer acceptors. When blended with a wide-bandgap polymer donor, the DCNBT-IDT-based all-PSCs achieve a remarkable power conversion efficiency of 8.32% with a small energy loss of 0.53 eV and a photoresponse of up to 870 nm. Such efficiency greatly outperforms those of N2200 (6.13%) and the naphthalene diimide (NDI)-based analog NDI-IDT (2.19%). This work breaks the long-standing bottlenecks limiting materials innovation of n-type polymers, which paves a new avenue for developing polymer acceptors with improved optoelectronic properties and heralds a brighter future of all-PSCs.

Synthesis of dipolar molecular rotors as linkers for metal-organic frameworks

We report the synthesis of five dicarboxylic acid-substituted dipolar molecular rotors for the use as linker molecules in metal-organic frameworks (MOFs). The rotor molecules exhibit very low rotational barriers and decent to very high permanent, charge free dipole moments, as shown by density functional theory calculations on the isolated molecules. Four rotors are fluorescent in the visible region. The linker designs are based on push-pull-substituted phenylene cores with ethynyl spacers as rotational axes, functionalized with carboxylic acid groups for implementation in MOFs. The substituents at the phenylene core are chosen to be small to leave rotational freedom in solids with confined free volumes. The dipole moments are generated by electron-donating substituents (benzo-1,3-dioxole, benzo-1,4-dioxane, or benzo-2,1,3-thiadiazole annelation) and withdrawing substituents (difluoro, or dicyano substitution) at the opposite positions of the central phenylene core. A combination of 1,4-dioxane annelation and dicyano substitution generates a theoretically predicted, very high dipole moment of 10.1 Debye. Moreover, the molecules are sufficiently small to fit into cavities of 10 Å3. Hence, the dipolar rotors should be ideally suited as linkers in MOFs with potential applications as ferroelectric materials and for optical signal processing.

Cyano-substituted benzochalcogenadiazole-based polymer semiconductors for balanced ambipolar organic thin-film transistors

Two new cyano-substituted benzochalcogenadiazoles were copolymerized with bithiophene, and the polymers show well balanced ambipolarity in transistors.

Organometallic Group 11 (CuIII , AgIII , AuIII ) Complexes of a trans-Doubly N-Confused Porphyrin: An "Expanded Imidazole" Structural Motif

Complexation of group 11 metal cations with an α-bis(phenylthio)-substituted trans-doubly N-confused porphyrin (trans-N₂ CP_SPh : 4) afforded a series of square-planar trivalent organometallic complexes (i.e., Cu-H4, Ag-H4, and Au-H4). The X-ray crystal structures of the complexes revealed highly planar core geometries along with the presence of peripheral amine and imine nitrogen sites of the pyrrolic moieties. NMR, UV/Vis absorption, and magnetic circular dichroism (MCD) spectroscopies suggested the 18 π-electron aromaticity of the complexes. The aromaticity was also fully analyzed by various theoretical methodologies such as nucleus-independent chemical shift (NICS) and anisotropic induced current density (ACID) calculations. The central metal affects the amphiprotic character of the complexes possessing both pyrrolic amino nitrogen and imino nitrogen atoms at the periphery, which was examined by the photometric titration with trifluoroacetic acid (TFA) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), respectively. The inherent acidity of the complexes was followed in the order; Cu-H4>Au-H4>Ag-H4 and that of basicity was Au-H4>Ag-H4>Cu-H4. The complexes could be considered as an "expanded imidazole" structural motif.

Dicyanobenzothiadiazole Derivatives Possessing Switchable Dielectric Permittivities

Benzothiadiazoles are important electron acceptors and are frequently employed as electron-deficient components of donor-acceptor polymers. We report the effect of nitrile functionalities on the reactivity, steric hindrance, optoelectronic properties, and dielectric permittivity in dicyanobenzothioadiazole (DCNBT). Dielectric spectroscopy in the bulk and in solution assisted by DFT-calculations revealed that these molecules can be engineered to engender maximum values of the dipole moment and of dielectric permittivity due to the strong electron-withdrawing effect of the nitrile groups. The self-assembly in the bulk was investigated by X-ray scattering performed on single crystals, fibers (2D-WAXS), and thin films (GiWAXS). Combining these results, we found a switching of dielectric permittivity of the 4,7-alkylthienyl-substituted dicyanobenzothiadiazole at the transition from the liquid crystalline to the isotropic phase with values capable of competing with the best known rodlike liquid crystals.

Organic Electron Acceptors Comprising a Dicyanomethylene-Bridged Acridophosphine Scaffold: The Impact of the Heteroatom

Stable two-electron acceptors comprising a dicyanomethylene-bridged acridophosphine scaffold were synthesized and their reversible reduction potentials were efficiently tuned through derivatization of the phosphorus center. X-ray crystallographic analysis combined with NMR, UV/Vis, IR spectroscopic, and electrochemical studies, supported by theoretical calculations, revealed the crucial role of the phosphorus atom for the unique redox, structural, and photophysical properties of these compounds. The results identify the potential of these electron deficient scaffolds for the development of functional n-type materials and redox active chromophores upon further functionalization.

Organofluorine chemistry: Difluoromethylene motifs spaced 1,3 to each other imparts facial polarity to a cyclohexane ring

2,2-Dimethyl-5-phenyl-1,1,3,3-tetrafluororocyclohexane has been prepared and characterised as an example of a facially polarised cyclohexane containing 1,3 related CF₂ groups. The dipolar nature of the ring arises from the axial orientation of two of the C-F bonds pointing in the same direction, and set by the chair conformation of the cyclohexane. This electrostatic profile is revealed experimentally both in the solid-state (X-ray) packing of the rings and by solution (NMR) in different solvents. A computationally derived electrostatic profile of this compound is consistent with a more electronegative and a more electropositive face of the cyclohexane ring. This placing of CF₂ groups 1,3 to each other in a cyclohexane ring is introduced as a new design strategy which could be applicable to the preparation of polar hydrophobic cyclohexane motifs.

Polarity-Tunable Host Materials and Their Applications in Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes

A series of polarity-tunable host materials were developed based on oligocarbazoles and diphenylphosphine oxide, and their polarities can be tuned through increasing distance of acceptor and donor units. Density functional theory calculations were employed, and photoluminescence spectra in different polar solvents were measured to illustrate different polarities of these host materials. As CZPO has relatively stronger polarity, electroluminescence (EL) spectrum of solution-processed device based on 6 wt % PXZDSO2:CZPO is 7 nm red-shifted relative to that of other host materials based devices. Besides, a comparable impressive external quantum efficiency (EQE) value of 18.7% is achieved for an evaporation-processed yellow device consisting of FCZBn, which is superior to that of the device based on CBP (4,4'-dicarbazolyl-1,1'-biphenyl) (17.0%), and its efficiency roll-off is also obviously reduced, giving an EQE value as high as 16.3% at the luminance of 1000 cd/m². In addition, from CZPO to FCZBn as the polarities of host materials decrease, EL spectra of solution-processed devices based on DMAC-DPS emitter blue-shift constantly from 496 to 470 nm. The current work gives a constructive approach to control EL spectra of organic light-emitting diodes with a fixed thermally activated delayed fluorescence emitter by tuning the polarities of host materials.

Dimension-controlled assemblies of modified bipyrroles stabilized by electron-withdrawing moieties

Benzoyl-substituted bipyrroles possessing aliphatic chains were synthesized and formed a variety of dimension-controlled assembled structures as mesophases using various intermolecular interactions.